Additivation of substrates, in particular packaging substrates (e.g. cellulosic substrates) with fluorochemicals to impart grease, oil, wax and solvent repellence has been known for some time.
These compounds are used for the manufacture of substrates suitable to be used with fat foods for short periods (clamshells or bags for hamburger, fast food products, pop-corn, small cardboard tubs for chips, etc.) and for longer periods (flexible packages for fat foods, food for dogs and cats, biscuits, etc.).
Among commercially available fluorochemical modifiers well-suited for this application, those based on (per)fluoropolyethers have drawn increased attention, due to their better HSE and toxicological profile with respect to perfluoroalkyl-containing counterparts and their acceptable oil and water repellence properties.
Among techniques for conferring oleo-repellence to substrates, in particular cellulosic substrates, treatments with (per)fluoropolyether derivatives comprising perfluorooxyalkylenic chains in a polyurethane backbone (see e.g. EP 1273704 A (AUSIMONT SPA (IT)) Jan. 8, 2003 and EP 1369442 A (Dec. 10, 2003) Dec. 10, 2003) or with (per)fluoropolyether derivatives comprising phosphate groups (as taught e.g. in U.S. Pat. No. 5,691,000 (AUSIMONT SPA (IT)) Nov. 25, 1997, EP 1138826 A (AUSIMONT SPA (IT)) Oct. 4, 2001, EP 1273704 A (AUSIMONT SPA (IT)) Jan. 8, 2003, and EP 1371676 A (SOLVAY SOLEXIS S.P.A.) Dec. 17, 2003) or with (per)fluoropolyether derivatives having carboxyl groups (as shown in EP 1484445 A (SOLVAY SOLEXIS SPA (IT)) Dec. 8, 2004 and EP 1489124 A (SOLVAY SOLEXIS SPA (IT)) Dec. 22, 2004) are known.
Said (per)fluoropolyether derivatives are typically incorporated into the cellulose substrate during the manufacture itself of the substrate at the paper mill. Actually, said derivatives are generally introduced in formulations either employed in size-press treatment, coating treatment, calender water box treatment or in wet-end treatment in the paper machines.
A paper machine is actually a large de-watering device consisting generally of a head box, a wire section, press section and dryer section wherein starting from a dilute suspension of fibres, and possibly fillers, dyes and other chemicals, which is homogenously fed onto a fine mesh through which the water drains, the fibres web is conveyed onto subsequent pressing and drying stages.
In the wet-end treatment, the (per)fluoropolyether derivatives are introduced in the initial fibres suspension dispersion and caused to deposit onto the fibres during web formation.
When used in the size-press treatment, the (per)fluoropolyether derivative is caused to impregnate the fibres web of paper by passing this latter into a sizing liquid pond located above a roll nip. As a result, the paper web absorbs the sizing liquor including the (per)fluoropolyether derivatives.
When used in a coating treatment, the (per)fluoropolyether derivative is caused to impregnate the fibres web of paper by passing this latter through a coater, typically rod or metering blade. As a result, a thin film of coating of the (per)fluoropolyether derivative is applied to the surface of the paper web.
When used in a calendar water box, the (per)fluoropolyether derivative is caused to impregnate the fibres web of paper by passing this latter through a calender stack equipped with a water box. The water box applies a dilute solution of (per)fluoropolyether derivative to the calender roll which is then transferred to the paper web.
Nevertheless, in all these processes, a significant amount of (per)fluoropolyether derivatives is caused to penetrate the entire thickness and surface of the substrate, while water and oil repellence are required only at the surface of certain areas of the manufactured substrates, in particular of paper. Also, (per)fluoropolyether derivatives are lost with broke and trimmed papers. Actually, for cellulosic substrates, (per)fluoropolyether derivatives costs contribution represents a high fraction of the final cost of the paper: even if present in amounts ranging from 0.1 to 1% by weight with respect to the dry fibres, (per)fluoropolyether derivatives represent from 10% up to 50% of the total costs (including the process water, the energy and the cellulose). It is thus essential to reduce consumption of these additives, their recycle and improper sizing.
Moreover, said (per)fluoropolyether derivatives might interfere with glueability and printability of the treated substrates. As the treatments performed at the paper mill are not selective and the whole thickness and surfaces are completely modified, glueability and printability of paper obtained thereof are poor, so that final parts are generally provided with additional coatings/surface treatment for overriding these drawbacks.
Need is thus felt to provide a novel method for imparting grease, oil and water repellence to substrates, in particular packaging substrates which would be more economical and provide a more tailored application of the additive on the substrate, while maintaining glueability and printability where required for manufacturing final packaging, bags and the like.